The present invention is directed to an internal combustion (IC) engine. In particular it relates to an internal combustion engine which utilises oxygen and fuel for heat supply and heated water as the working medium for gas expansion in the cylinder. The invention is further directed to a mechanism which transfers. heat from exhaust gas and coolant to water which is recycled back into the combustion chamber.

BACKGROUND OF THE INVENTION

Known internal combustion engines in general can effectively transform about one third of the chemical energy stored in fuel into useful work. About two thirds of the remaining energy is rejected to the environment as secondary heat. A small portion of the fuel is left unbumed or not fully oxidized causing carbon monoxide, hydrocarbon and particulate matter (PM) emissions that are discharged into the atmosphere.

hi view of the high level of fuel prices it is desirable to improve the efficiency of IC engines convert a greater proportion of the energy stored in the fuel to useful work than the current one third conversion efficiency.

Concurrently, it is also desirable to approach full oxidation of the fuel, hi theory, near- full oxidation of fuel will virtually transform all the chemical energy into heat, water and carbon dioxide.. This in turn will leave very minimal amounts of carbon monoxide, hydrocarbon and particulate matter.

hi maximizing the release of heat from fuel, challenges also come in the form of oxides of nitrogen (NOx) emission and heat management of the engine. Accelerated and maximum heat release is likely to cause combustion temperature above 2000 Kelvin a temperature at which NOx is likely to form. The formation of NOx currently requires expensive exhaust aftertreatment systems to meet the increasingly more stringent current and future emissions legislation. Conventional internal combustion engines tackle the problem of heat management by introducing water coolant filled radiators cooled by ambient air. Very little research has been done to tackle this problem at the source of the problem itself; the inability of the engine itself to transform all the released heat into useful work, thus resulting less heat from being rejected to the coolant and exhaust gas.

hi maximizing the heat being converted into useful work, it should of course be noted that whenever the one third energy conversion efficiency is increased, the two thirds portion of the heat rejected to the surroundings will be decreased proportionately. If the two thirds portion is decreased to the very minimum, it is not impossible for radiator of a typical passenger car to decrease significantly in size or to be totally omitted. It is also possible that the exhaust gas exiting the tailpipe may approach the temperature of the ambient air.

Even if it is possible to improve the efficiency of combustion, there will still be energy being wasted as secondary heat and discharged to the environment. It is therefore also desirable to enable the remaining heat transferred to the coolant and exhaust gas to be recycled back into the combustion chamber in following combustion cycles.

SUMMARY OF THE INVENTION

One aspect of the present invention provides an internal combustion engine comprising: a cylinder; a piston located in the cylinder and connected to a crankshaft for reciprocal motion with respect to the cylinder and defining a combustion chamber within the cylinder; a fuel injector tb selectively inject fuel into the combustion chamber; an oxidising agent injector to selectively inject oxidising agent into the combustion chamber; a water injector to selectively inject water into the combustion chamber; an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber; wherein the engine is configured such that water is injected by the injector after combustion of the fuel has commenced.

A second aspect of the present invention provides a method of operating an internal combustion engine comprising: a cylinder; a piston located in the cylinder and connected to a crankshaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder; a fuel injector to selectively inject fuel into the combustion chamber; an oxidising agent injector to selectively inject oxidising agent into the combustion chamber; a water injector to selectively inject water into the combustion chamber; and an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber; the method comprising the steps of: a) injecting oxidising agent into the combustion chamber b) injecting fuel into the combustion chamber c) combusting the fuel in the combustion chamber d) injecting water into the combustion chamber after combustion has commenced.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of an internal combustion engine according to one embodiment of the present invention; Figure 2 is a perspective view illustrating the layout of a cylinder of the internal combustion engine of figure 1;

Figure 3 is a diagram illustrating the cycle of the engine of figure 1; and

Figure 4 is a schematic diagram illustrating another embodiment of the internal combustion engine of the present invention. . . DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 schematically illustrates a single cylinder embodiment of the internal combustion engine of the present invention indicated generally at 10 along with its ancillary heat exchange system.

The internal combustion engine 10 comprises a cylinder 12 in an engine block 11, a piston 14 in the cylinder defining a combustion chamber 13, an exhaust valve 16 in an exhaust port 17 of a cylinder head 36, a crankshaft 18 and a connecting rod 20. An oxidising agent (in this embodiment oxygen gas 20), fuel (in this embodiment diesel 22) and water 24 are injected into the cylinder through the use of oxygen, fuel and water injectors 26, 28, 30 respectively, and controlled electronically by an engine ECU (not shown). The piston has a depression in its upper surface defining a piston bowl 15.

Fuel and oxygen are ignited through the use of compression ignition in this embodiment, hi other embodiments spark ignition may be used, with a spark plug being provided in the cylinder head. The engine 10 is operated in a two stroke cycle in which the downward stroke comprises an expansion stroke and the upward stroke comprises a hybrid of initially an exhaust stroke, followed by a compression stroke.

Oxygen (preferably at 90% + purity) is supplied from a compressed oxygen tank 32. In other embodiments an oxygen generator may be used (see figure 4). The oxygen gas 20 is pressurized to enable it to be introduced during compression stroke. In this embodiment, a separate oxygen generator (not shown) is needed to generate oxygen from the ambient air. The oxygen is. later compressed into the oxygen tank at around 170-250 bar. The oxygen supplied through compressed oxygen tank 32 makes this embodiment particularly applicable for land or sea vehicle with restricted space that lacks room for an onboard oxygen generator.

The engine 10 further comprises a coolant circuit 34 of a standard water/glycol that is circulated through the engine block 11 and cylinder head 36 of the engine 10 to a heat exchanger 38 (discussed in more detail below) by a water pump 40. Coolant temperature is monitored by a temperature sensor 35. The coolant circuit is advantageously pressurized to 3 bar in order that the temperature can be maintained at 130 ⁰ C. The temperature is controlled by varying the speed of the water pump 40. The engine further comprises a lubrication oil circuit 42 that introduces lubricants into the crankcase of the engine 20 and is also cooled by the heat exchanger 38.

A water pipe 44 takes water 24 from a water tank 25 and passes it through the heat exchanger 38 to remove heat from the coolant in coolant circuit 34 and from the lubrication oil in oil circuit 42. The water 24 is compressed by a high pressure water pump 46 and is passed through a high pressure heat exchanger 48 described in more detail below, before being injected under pressure into the cylinder 12 by the water injector 30.

Secondary heat from exhaust gas exits the cylinder after combustion via the exhaust port 17 and enters the heat exchanger 48 placed immediately downstream of the exhaust valve 16. This recovers a substantial proportion of the secondary heat from the exhaust gas and transfers it to the pressurised water 24. At the same time, some heat needs to be retained in order to keep a 2-way catalytic converter 50 at a temperature above 300 ⁰ C for optimum pollutant conversion efficiency. For this reason, the catalytic converter 50 is located immediately downstream of the high pressure heat exchanger 48.

Remaining secondary heat in the exhaust gas is recovered using a second heat exchanger in the form of a condenser 52. This recovers water 24 from the exhaust gas and is positioned within the water tank 25. hi maximizing the amount of water recovered from the exhaust gas, there should be a significant temperature difference between the exhaust gas and the heat exchanger 48. hi other words, the pipe section after the catalytic converter is significantly cooled down by condenser 52. This requires insulation 54 preferably made of ceramics, to be introduced in between the catalytic converter outlet and an exhaust pipe 55 leading to the second heat exchanger In maximizing the water to be recovered from the exhaust gas, a further substantial temperature difference is created by placing the condenser 52 inside the water reservoir 25. For this purpose, the water in the water reservoir is kept at 30-40 ⁰ C by having rninimum water volume to be stored in the condenser 52. Once the water has condensed and accumulated at the bottom of the condenser 52 it is circulated back into the water pipe 44 via a second pipe 56, the flow in which is controlled by a electronically controlled valve 58.

About 20% of the water may not be recovered from the exhaust gas so the water storage or water tank 25 needs to be refilled from time to time. This ratio is chosen to ensure pollutants dissolved by the water will not on the one hand build up to a concentration that may cause significant material deterioration to the pipe 55 and tank walls, and on the other hand refills do not become too frequent.

Once as much of the heat from the exhaust gas as is feasible has been recovered, the exhaust gas exiting the tail pipe is typically around 50-70 °C. As much of the heat has been taken out from the exhaust gas, it has a relatively low velocity as it exits the tailpipe.

hi this embodiment the crankshaft 18 outputs to a continuous variable transmission 60, but in other embodiments other suitable transmission systems may be used.

Figure 2 shows the layout of a variant of the cylinder 12 in more detail. It can be seen that the cylinder head 36 comprises two exhaust valves 16 in order that the exhaust gases may exit the combustion chamber 13 in a relatively unhindered manner. The cylinder further comprises two water injectors 30 that are directed upwardly and are positioned in the wall of the cylinder (not shown in Figure 2) so as to spray the water in the direction of hot spots in the cylinder, and in particular the exhaust valves 16 and area between the exhaust valves (the exhaust valve bridge), hi order for the geometry of this arrangement to be feasible, recesses 58 are provided in the piston 14 at locations corresponding to the water injectors 30 so that the flow of water from the injector 30 is not impeded when the piston is around top dead centre (TDC). Also illustrated in figure 2 is a conventional diesel fuel injector 28 which is flanked either side by two oxygen injectors 26 that are positioned so as to promote the optimal mixing of oxygen with the diesel fuel in the cylinder.

Referring back to Figure 1, with water being injected upward onto the cylinder head 36 hot spots, the heat rejection to the coolant is significantly lower by comparison with a conventional IC engine. Even so, engine coolant is still needed to cool off critical areas like exhaust valve bridge, oxygen injectors 26 and cylinder head flame face. Cooling of cylinder block 11 is still needed but it is limited to only the top part of the wall of the cylinder 12.

Since there is still significant heat being rejected to the engine coolant, there is significant heat that can be recovered and delivered back into the combustion chamber. In a variant of the engine 10 of Figure 1, the coolant radiator is placed inside the water tank 25 to ensure large temperature difference between the engine coolant and the water inside the reservoir which also serves as the cooling medium.

A temperature sensor 19 is located near the hottest spot at the cylinder head to provide temperature reading to the ECU for feedback. The control system of the ECU controls the flow rate of the coolant pump 40 and thus the. amount of coolant entering, and exiting the engine can be controlled to ensure optimum heat rejection from the coolant to the water reservoir and also from the combustion heat to the water coolant.

With reference to figure 3 the cycle of the engine operation can be explained as followed.

As the expansion stroke takes place, the exhaust valve 16 is opened (EVO) just before bottom dead centre (BDC) or at BDC (180° crank angle). There is no clear need for the exhaust valve 16 to be opened much earlier for "blowdown" operation as the use of substantially pure oxygen 20 (or 90% + pure oxygen) reduces the charge mass by up to 78% relative to other conventional (IC) engines. Moreover, the use of substantially pure oxygen eliminates the need to run the engine lean which is normally required in conventional diesel engine. To minimize oxygen consumption, a stochiometric oxygen to fuel (OF) ratio is preferred. However, to maximize the combustion efficiency, the oxygen can be increased by up to 20% from stochiometric value. A wide range lambda sensor (not shown) can be used to monitor the OF ratio during the engine operation.

As the exhaust valve 16 is opened, the combustion byproducts together with the injected water (see below), which is now in vapor state, is discharged to the exhaust port 17 and later to the atmosphere. The amount of residual charge remaining in the cylinder is controlled by adjusting the crank angle at which the exhaust valve 16 is closed.

The crank angle of the cycle where the exhaust valve 16 is closed also determines the effective compression ratio of the engine 10, and can be advanced or retarded from the baseline using a suitable variable valve timing mechanism controlled by the ECU. Such variation enables the compression work to be optimized depending on engine rpm and load. Compared to conventional IC engines, the compression work in this embodiment of the present invention is limited and it is only needed to raise the cylinder temperature to about 150-200 °C above the autoignition temperature.

By limiting the compression work, it is also possible to keep the cylinder pressure low by comparison with a conventional diesel IC engine. With maximum cylinder pressure being kept at 100-120 bar instead of the more usual 180-200 bar, engine parts can be designed with less structural reinforcement.

The exhaust valve typically closes (EVC) between 1/3 to 4/5 of the total compression stroke (i.e. a crank angle of between 216° and 324°). Compared to a conventional four stroke engine which uses the entire compression stroke doing compression work, the engine of the present invention utilizes only 4/5 to 1/3 of the upward stroke for compression work. This in turn consumes less engine power and cylinder pressure can be kept low when the diesel fuel 22 is being ignited. With this valve 16 opening and closing arrangement, it is possible to optimize the effective compression ratio in accordance to engine rpm and load. At the same time, the expansion ratio can be maximized as the exhaust valve will only be opened close to BDC. Over the range of rpm and load, the exhaust valve is only opened to enable the cylinder pressure at BDC to be kept below 5 bar. By keeping the cylinder pressure low at BDC, there is no significant resistance to the piston 14 as the piston moves up.

As the exhaust valve 16 is opened, the exhaust valve lift may also be varied depending on engine rpm and load. By varying the exhaust valve 16 lift to relatively lower lift than what is normally done in other conventional IC engines (e.g. down as low as 1 mm), it is possible for higher content of exhaust gas to be retained without having to close the exhaust valve 16 early. In retaining the exhaust gas inside the cylinder, a

-significant amount of heat can be retained which is useful in raising the cylinder 12 temperature above the autoignition temperature in the next compression stroke. As hot exhaust gas is retained in the cylinder 12, it provides both mass and an elevated charge temperature which can further minimize compression work required to raise the cylinder temperature about 150-200 ⁰ C above the fuel autoignition temperature.

The variation of lift described in the previous paragraph may be done without any changes to the duration of exhaust valve opening. In the prior art (for example the BMW Valvetronic system) the exhaust valve lift is varied in proportion to changes to the valve opening duration. By having low valve lift combined with constant and long exhaust valve opening duration, it is possible to retain the exhaust gas without significant increase in cylinder pressure as the piston moves upward.

A ID simulation has shown that it is possible to lower the valve lift for the purpose of retaining the exhaust gas without causing the cylinder pressure to significantly increase. This demonstrates that there is no significant increase in pumping work. It is believed this phenomenon may be caused by the relatively lower charge mass due to the use of oxygen rather than ambient air.

Once the exhaust valve 16 is fully closed, about 50-70% of the total oxygen required in the cycle is injected at high pressure between OVOl and OVCl. The first gas injection will take place around 30 degree before TDC and occurs rapidly, e.g. in a 10°-20° range.

This will be followed by fuel injection commencing at 5-15° before TDC (FVO) and ceasing at 5-10° after TDC (FVC). The diesel fuel ignites substantially immediately after leaving the fuel inj ector 28.

The remaining 30-50% of the total oxygen required is injected from 2-3° before TDC (OVO2) and ceasing at 5-15°. This enables the oxygen used up for fuel oxidation to be replaced. With such a powerful injection pressure, much of the combustion byproduct is also believed to be cleared out from the piston bowl 15. This measure makes it possible to have oxygen constantly available inside the piston bowl 15 for complete fuel oxidation.

With the use of oxygen stratified together with diesel substantially inside the piston bowl 15, the heat release is significantly faster compared to conventional diesel engine and the ignition delay is believed to be low. Firstly, since the compression work is minimised, the cylinder pressure is around 30-40 bar and this will significantly cause the diesel boiling point not to be raised as high as it will be when subjected to cylinder pressure of 70-100, bar which is normally found in conventional diesel IC engine. As the boiling point drops, the injected diesel fuel vaporizes relatively earlier. Secondly, once it vaporizes, the fuel easily finds oxygen as it is in plentiful supply by being stratified in the piston bowl 15.

With minimum ignition delay in an oxygen rich combustion chamber, the amount of premixed combustion will be less. Thus there is less sudden heat release that will be detrimental to engine components. The amount of diesel fuel being combusted through diffusion combustion is believed to be high. Thus it is possible to further control the release of heat by controlling the flow rate of diesel fuel coming out of the injector 28. Water is injected from the water injectors 30 once 50% mass of fuel has been burned which occurs at around 0-15° after TDC. This differs from the prior art in which water is injected before fuel is ignited. By introducing water only after 50% mass fraction burn is reached, there is minimal flame suppression by water, which can otherwise cause partial oxidation that is detrimental to fuel consumption and emission formations. To further minirnize flame suppression, the water is injected upwards toward the cylinder head 36, preferably toward hot spots as described above. In the prior art the water injectors inject water into the piston bowl.

Though fuel oxidation, flame development and heat release happen relatively quickly, it takes time for all this process to occur. By the time water molecules reach the flame development region, typically the maximum amount of fuel has been burned and maximum amount of heat has been released in the combustion chamber. Moreover, with the cylinder temperature quickly rising, especially near the flame development region, it is likely that the water molecules to have turned from liquid to vapor state. This reduces the flame suppression rate by the water.

The amount of water injected into the cylinder 12 depends mostly on the need to limit the maximum cylinder temperature to 1800 Kelvin. Depending on the engine rpm and load, the maximum cylinder temperature can occur at between 0° to 45° crank angle.

It is also desirable to keep the exhaust gas temperature at 1000 Kelvin or above at the point where the exhaust valve 16 is to be opened.

Another criterion for the total water mass to be injected in every cycle is the maximum allowable material temperature limit. To minimise the occurrence of engine parts overheating, the temperature 19 sensor is utilised to monitor heat build-up in the combustion chamber. During the entire range of the engine operation, if the heat sensor senses the material temperature to be close to the material limit, extra water mass is injected to cool down the surface temperature.

As a result of these considerations, the mass of water to be injected is in the range of approximately 3 to 15, typically 5 to 12 times the amount of mass of fuel injected, hi this context, the flow rate of the fuel injector 28 is timed to enable as much as 15 times the water mass to be injected within approximately 20-30° of crank angle after the water injection starts, even when the engine is operating at its maximum operating speed.

As the combustion heat is being absorbed by the injected water 24. The water quickly changes state from liquid to vapor state. Expansion occurs when water changes state from liquid to vapor, which causes the cylinder pressure to increase and the piston to be pushed down to BDC.

Water 24 to be injected is heated in the high pressure heat exchanger 48 potentially until it is close to its boiling point. The high pressure positive displacement water pump 46 pressurizes the water line enabling the boiling point to be raised significantly above 100°. With the water pressure raised to 150 bar, the water boiling temperature is raised from 100 °C to approximately 340 ⁰ C. This makes it possible for the water to be heated close to 300 °C without causing the water to turn from liquid to vapor.

It is known that the pumping work required to raise the pressure inside a constant volume is 10 times less for water in liquid state if compared to water in vapor state. This is why it is important for water to remain in liquid state until the water is discharged into the combustion chamber 13.

With a temperature as high as 300 °C, the cylinder pressure of below 100 bar lowers the water boiling point from 340 °C to slightly below 300 °C. Considering that water absorbs heat from the combustion, the water temperature will be raised further causing the water to change state from liquid to vapor almost immediately after it leaves the injectors 30.

In other embodiments, it is possible to use a slightly lower water temperature to enable the injector material to withstand the elevated temperature of water. In this scenario, the time taken for the water to change state from liquid to vapor will be relatively longer. However, the same amount of water will be able to reduce the cylinder temperature to a lower temperature compared to when the higher temperature injected water.

Considering gas expansion, the expansion of water in vapor form is about 2.5 times the expansion of carbon dioxide when subjected to the same temperature. When compared to Nitrogen, the expansion of water in vapor form is about 1.5 times. This results in water in vapor form being a better medium for gas expansion in a reciprocating engine and in turbines.

In terms of heat absorption, water in liquid form has a heat capacity of 4.18 kJ/(kgK). Water in vapor form has a heat capacity of 1.52 kJ/(kgK) at 100 °C. Carbon dioxide gas has a heat capacity of 0.63 kJ/(kgK). Nitrogen gas has a heat capacity of 0.74 kJ/(kgK). Thus, water in both liquid and vapor form can absorb heat much better, compared to other gases which are normally present in conventional IC engines.

Water has the further advantage of being cheap and abundant provides an improved way for minimizing heat being transferred to the surrounding metal and engine coolant of engine 10. As more heat is absorbed by water, more work is done on the piston 14 leaving less heat to be rejected to the atmosphere via exhaust gas and engine coolant. Furthermore, the portion of heat that is rejected to the engine coolant and exhaust gas, is recovered to some extent by the heat exchanger 38.

Figure 4 illustrates an IC engine 110 according to a second embodiment of the present invention in schematic form. The basic layout and principles of operation of the engine 110 are similar to those of engine 10, and where possible, similar parts are labelled by like numerals, but with the addition of the prefix "1". Only differences with respect to the first embodiment are discussed in depth.

The engine 110 is adapted for use in applications where a greater amount of space is available by comparison with engine 10, such as in static electric generators and large ships. Consequently it may be used to burn heavy fuel oil, where the increased availability of oxygen and reduced amount of nitrogen in the combustion process minimises the amount of NOx produced, which has traditionally been, a problem with this fuel. In addition the high sulphur content of such fuels is dissolved in the injected water rather than being emitted as sulphur dioxide.

As the injected water dissolves sulphur dioxide, sulphuric acid will be formed which can be detrimental to engine parts and the water pipeline. This requires the water 24 and 124 to have pH higher than 7 through addition of additive or alkali by a suitable injection system (not shown). Such additive or alkali solution is required to neutralize sulphuric acid formation in the water line.

The greater space availability enables a non-cryogenic oxygen generator (not shown) to be used in situ. Gas pressure exiting the oxygen generator is normally low at slightly above atmospheric pressure. Through line 172, the oxygen will be fed into a turbocharger 170 where the gas pressure will be raised further prior to being compressed by a reciprocating compressor to 25 bar. An electronically controlled low pressure electric water pump 176 will draw in condensed water from the condenser 152 and the water will exit the nozzle 178. The turbocharger 170 sucks in both oxygen and water into the turbo unit for further compression. As gas compression will also elevate the charge temperature, the supplied water cools off the charge.

The oxygen is fed in a direction Y where it is then further compressed to the desired injection pressure by a reciprocating pump 180 driven from the crankshaft 118 by CVT 160. The CVT 160 enables the reciprocating pump speed to be varied at various engine rpm and load. Such a variation in reciprocating pump speed is important during idle where the turbocharger 170 does not contribute much in raising the charge pressure. In this embodiment, the crankshaft has a further output to a propeller 182

A secondary air pump 174 supplies ambient air to the turbocharger turbine outlet. Turbine outlet is chosen as the point of entry for the secondary air as this will enable the secondary air to mix well with the exhaust gas prior to the charge entry to the catalytic converter. A one way valve (not shown) prevents exhaust gas from entering the secondary air pump. The supplied ambient air provides supplementary oxygen to the 2 way catalytic converter 150 which is useful in increasing the catalyst conversion efficiency involving hydrocarbon and carbon monoxide. Water exiting the heat exchanger 138 also flows through the turbocharger 170 turbine unit. As the turbine unit is constantly in contact with the exhaust gas, significant heat can be extracted from the turbine which further elevates the water temperature.

It will be appreciated that the engines of the present invention provides numerous advantages over the prior art. Primarily , the use of water in the combustion cycle that has been heated by exhaust gases enables more efficient utilisation of the fuel, the use of higher concentrations of oxygen in the oxidising agent minimises harmful emissions (in particular particulates and NOx) and enables fuel burn to be better controlled and cheaper two-way catalytic converters to be used.

It will be understood that numerous changes may be made within the scope of the present invention. The engine may be used and adapted to burn other fuels such as petroleum (gasoline), biodiesels, bioethanols, compressed natural gas and methanol. The engine may be adapted to run on a four stroke cycle and may use multiple cylinders and pistons in various configurations, such as V, W or boxer configurations. Presently, inline six and boxer four cylinder configurations are preferred due to then- improved balance. In addition, an inline four cylinder engine with a 90 degree crankshaft configuration is envisaged (instead of flat plane crankshaft). This enhances smoothness and may eliminate the need for balancer shafts. The engine may operate using ambient air as the oxidising agent, or with oxygen lower than the preferred 90% purity, and many benefits from using water injection are still realised.

As will be appreciated the fuel is injected directly into the combustion chamber. As will be appreciated the water is injected directly into the combustion chamber. As will be appreciated the oxidising agent is injected directly into the combustion chamber. As will be appreciated the injected oxidising agent is the sole source of oxidising agent after start up (e.g. the engine does not include traditional inlet valves).

hi some embodiments a water temperature sensor can be provided to determine the temperature of the water just prior to injection. In some embodiments two fuel injectors can be provided.

A first fuel injector may inject a first fuel of a higher cetane value prior to a second fuel injector injecting a second fuel of a lower cetane value. In some embodiments both fuels are ignited by auto ignition. Injecting a first fuel of a higher cetane value requires a lower auto ignition temperature which allows more energy to be extracted from the previous power stroke. Once the first fuel has started to burn the temperature within the combustion chamber increases, in particular to a temperature at or above the auto ignition temperature of the second fuel, which can then be injected and will auto ignite. Thus preferably the first fuel is injected when the combustion chamber conditions are such as to be below the auto ignition temperature of the second fuel. In this way power can be produced by using low grade fuels, e.g. fuels with a low cetane value. Such fuels tend to be cheaper than higher grade fuels. The first fuel may be a high grade of fuel such as a diesel fuel. The second fuel may be a fuel derived from plants, such as a biomass fuel. The second fuel may be pyrolysis oil.